answer.code: In function ‘int main()’:
answer.code:25:24: error: expected identifier before ‘this’
   25 |         auto dfs = [&](this auto &&dfs, int v) -> void {
      |                        ^~~~
answer.code:25:24: error: expected ‘,’ or ‘...’ before ‘this’
answer.code: In lambda function:
answer.code:26:35: error: ‘v’ was not declared in this scope
   26 |             for (auto [to, id]: g[v]) {
      |                                   ^
answer.code:28:17: error: use of ‘dfs’ before deduction of ‘auto’
   28 |                 dfs(to);
      |                 ^~~
answer.code:37:17: error: ‘v’ was not declared in this scope
   37 |             pos[v] = all.size();
      |                 ^